YES(?,O(n^2)) Problem: +(x,+(y,z)) -> +(+(x,y),z) +(*(x,y),+(x,z)) -> *(x,+(y,z)) +(*(x,y),+(*(x,z),u)) -> +(*(x,+(y,z)),u) Proof: Matrix Interpretation Processor: dimension: 2 interpretation: [1 9] [0] [*](x0, x1) = [0 1]x0 + x1 + [5], [1 1] [0] [+](x0, x1) = x0 + [0 1]x1 + [2] orientation: [1 1] [1 2] [2] [1 1] [1 1] [0] +(x,+(y,z)) = x + [0 1]y + [0 1]z + [4] >= x + [0 1]y + [0 1]z + [4] = +(+(x,y),z) [2 10] [1 2] [2] [1 9] [1 1] [0] +(*(x,y),+(x,z)) = [0 2 ]x + y + [0 1]z + [9] >= [0 1]x + y + [0 1]z + [7] = *(x,+(y,z)) [1 2] [2 19] [1 1] [7 ] [1 1] [1 9] [1 1] [0] +(*(x,y),+(*(x,z),u)) = [0 1]u + [0 2 ]x + y + [0 1]z + [14] >= [0 1]u + [0 1]x + y + [0 1]z + [9] = +(*(x,+(y,z)),u) problem: Qed